CuX‐Stabilized NiO _x Interface Toward Efficient Flexible Perovskite Solar Cells

ABSTRACT NiO x has emerged as a commonly used hole transport material in p–i–n perovskite solar cells owing to outstanding p‐type characteristics and robust stability. However, the undesired redox reaction at the perovskite/NiO x interface significantly impairs the device performance and stability. Hence, we develop an anion–cation synergetic strategy to inhibit Ni 2+ oxidation and optimize the buried interface of perovskites. The cuprous cation (Cu + ) from CuX (X = Cl, Br, or I) layer suppressed the undesired Ni 2+ oxidation, while halogen ions passivated vacancy defects and modulated crystal growth of perovskites simultaneously, then achieving an excellent interface with quick charge transport and extraction. Furthermore, the beneficial effect of different anions on NiO x and perovskite layers is further quantified and revealed. Consequently, the optimized flexible triple‐cation and FAPbI 3 composition PSCs yield a power conversion efficiency (PCE) of 21.64% and 22.93%, respectively, along with notably improved device stability, maintaining 85% of the initial efficiency even after 6000 h storage. This work offers a reference approach to enhance the performance and stability of inverted flexible PSCs by an anion–cation synergetic strategy.